The components of a Proton Exchange Membrane (PEM) fuel cell Membrane Electrode Assembly (MEA) typically include a membrane, one or more catalyst layers and a gas diffusion layer. The membrane performs a proton transport function in the cell, and provides electronic isolation between anode and cathode, thus providing a means of keeping fuel and oxidant from mixing. Typically, the membrane is between 10 and 200 microns thick, and is prepared from ionomer resin. Representative of such structures are those described in Raistrick, U.S. Pat. No. 4,876,115.
The catalyst layers are generally included on both the anode and cathode. The catalyst is typically contained in a matrix of catalyst material and binder. The binder material can be ionomer, PTFE or other material to hold the catalyst powder in place. Typically, the catalyst layers are formed by suspending the catalyst particles in a solution of binder and solvents to form a slurry. The slurry is then coated, dried and cured. Alternative catalyst structures can be created that contain large surface areas of catalyst materials. The catalyst structures are typically between 2 and 50 microns thick.
The gas diffusion layers are included on both the anode and the cathode. Typically, the gas diffusion layers are constructed of carbon/graphite cloth, felt, paper, wire screen, or some other porous material. The diffusion layers are placed between the catalyst layers and the gas flow channels of the cell. The gas diffusion layer permits diffusion of reactant gas to the catalyst layer, and current collection from the catalyst layer. The gas diffusion layers are typically between 100 to 500 microns in thickness.
Currently, the construction of the above components into a fuel cell can be divided into two main categories, these involving attachment of the catalyst layer either to the membrane or to the gas diffusion layer. For example, Dhar, in U.S. Pat. No. 5,318,863, describes the preparation of solid polymer fuel cells having two gas diffusion electrodes, each coated on one side with a catalyst slurry and cured, followed by depositing a solution of proton conducting material on the central portion of the surface of each gas diffusion electrode and bringing the two electrodes together.
The present invention provides a process for the formation of the membrane component of the fuel cell by solution casting.
Specifically, the instant invention provides a method of manufacturing a membrane electrode assembly component comprising:
a. applying a catalyst slurry onto a removable decal;
b. drying the catalyst slurry;
c. applying at least one ionomer solution on the catalyst layer; and
d. at least partially curing the at least one ionomer solution layer; to form a membrane electrode assembly component.
The resulting coated electrodes are then brought together, preferably with a non-conductive gasket around the perimeter of the ionomer, to form a membrane electrode assembly.